Watercraft are often powered by outboard motors positioned at the stem of the craft. These motors have an internal combustion engine positioned within a cowling of the motor. Among other reasons, because the outboard motor is positioned at the stem of the craft, and because the motor is tiltable, it is desirable to keep the engine's size and weight to a minimum.
In order to keep the engine small, its various parts are typically mounted much closer to one another than might be the case with similar types of engines utilized in other settings. One problem which arises in these engines relates to keeping various of the components of the engine cool when they are so close to one another. The cooling problem is further aggravated by the fact that the engine is positioned within an enclosed cowling, trapping the heat therein.
It is especially important that the combustion chambers be cooled adequately, and be isolated from heat transfer from other portions of the engine. If the combustion chambers become too hot, the combustion efficiency is greatly reduced, lessening engine power output. In addition, if the combustion chambers become too hot, the lubricating oil may be scorched and burned, reducing its effectiveness. In addition, the cylinder walls, pistons or rings may be warped or damaged. The lubricating oil must be adequately cooled so that it does not break down and so that it does not transmit heat to the engine.
At the same time, when the engine is first started, it must heat up to a desired operating temperature in order for it to run efficiently. The lubricating oil is also desirably heated to a somewhat elevated temperature so that it flows freely throughout the engine.
A liquid cooling arrangement for an internal combustion engine which both cools the engine and yet provides for engine warm-up, is desirable.